Thread: Square the mortices or round the tenons?

Yer I square the mortise to.......................A traditional mortise and tenon fit squarely is the strongest joint of this type.

REgards Lou

The easiest way is to make the tenon octagonal, i.e. the two cheeks and three narrow edges at either end. This is very quick to do, and has the advantage of allowing excess glue to escape. That is, if I am not using floating tenons, in which case, I round over the tenon stock on the router table and then cut it to length. Theoretically, a square ended tenon would be marginally stronger; but I don't think this makes any difference in practice.

Rocker

Originally Posted by Rocker

but I don't think this makes any difference in practice.

Rocker

Gidday Rocker

In practice this makes a considerable difference. A squared mortise and Tenon joint that fits snugly is considerably stronger than the kinds of hybrid/Short-Cut joints you have listed.

If its strength your after then a traditional mortise and tenon joint is the GO! Fine Woodworking MAgazine stress tested rounded mortise and tenons champhored tenons in a round mortise loose tenons and traditional M&T's.

Under stress testing traditional M&T joinery proved significantly stronger. All the other joint types failed well before the traditional M&T's. Much to the suprise of the testers I might add.

REgards Lou

I voted for Round the tenon because, on those rare occasions when I use a router to cut a mortice, the quickest result is the obvious choice.

I rarely use a router to cut a mortice, however, because I find either a judicious use of the drill press or a swift bash with a chisel and mallet does the job. Rounding the tenon is also the obvious choice after cutting the mortice with the drill press.

Col

Originally Posted by Rocker

That is, if I am not using floating tenons, in which case, I round over the tenon stock on the router table and then cut it to length. Theoretically, a square ended tenon would be marginally stronger; but I don't think this makes any difference in practice.

Rocker

Agree 100% I use floating tenons that are router rounded, and as Rocker pointed out in practice (real world day to day practice) the difference would be so slight it wouldnt matter. In 3 weeks ill have my new Domino and rounded loose tenons will be all ill be using

NewLou,

I would not argue with you, or with FW for that matter. I merely maintain that it is rarely necessary for the joint to have the maximum possible theoretical strength; and that, if a rounded or chamfered tenon has only, say, 85% of the strength of a square one, it is normally speaking still plenty strong enough for its purpose.

Rocker

Rocker

Totally agree if the joinery is there simply for looks its a no brainer. However if the joinery is being used for a WorkBench or the like where Constant stress is a consideration Then the strongest joint I can use is my preference.

Even then I'm inclined to reinforce it with pocket holes or my own epoxy castings! (But thats just me)

REgardless It is interesting to have some kind of reference point in regards to the structural integrity of this kind of joinery........suprisingly the difference is significant

REgards Lou

Lou what is the FWW issue you have? I have FWW No 111 PG: 59 all about joint strength, and its surprising. These are cabinet doors and both loose tenon and mortice and tenon and under 1,200 psi started to open and snaped at 2,700psi and the surprise was two and three biscuits, the gap started at 1,700psi and snapped at 2,800 psi for the twin bisc and 3,000 for the tripple. So biscuits are the strongest for doors acording to that article

Lig

I was reading up about joinery on the FineWoodworkingNetwork for my workbench. I'll see If i can find the article again. In this particular test I'm pretty sure that the Biscuits proved the weakest type of joinery. IF interested I'll dig it up again and get some test specs

.....................Is always interesting for future reference.

From Fine Woodworking #148

TRADITIONAL TENON

Strength: Superior
RAte of Failure: Gradual
Strength after failure: Superior
Rigidity: Very stiff

Round Edged Floating Tenon

Strength: Excellent
RAte of Failure: Gradual
Strength after failure: Excellent
Rigidity: Stiff

Straight Edged Floating Tenon

Strength: Excellent
RAte of Failure: Abrupt
Strength after failure: Excellent
Rigidity: stiff

Twin #20 Biscuits

Strength: Good
RAte of Failure: Gradual
Strength after failure: Good
Rigidity: Moderate

This is a great little summary of the outcomes

REgards Lou

Round the tenon cos I do it my way

I do it Wongo's way.

Like driver and for basically the same reasons, I round the tenon. I'll also start the mortice using a bit'n'brace with a squaring jig if I'm feeling a tad darkside... besides the chisel, that's about as darkside as I want to get, too... Oh, for a powered morticer!

Totally agree if the joinery is there simply for looks its a no brainer.

How can a mortice and tenon be there simply for looks? You can't see it!!

I usually round the tenon if it's a mortice cut with the router. Have squared the mortice in the past when I'm being fussy.

I recall the results of another one of those 'tests'. They were specifically testing doors. The biscuit join was the strongest but it failed suddenly and completely. The mortice and tenon failed sooner but it hung together for longer.

I'm a round tenon.